• Applying Roundup to the Base of Lemon Tree Canopies: Preliminary Effects on Leaves, Flowers, Fruitlets, and Yield

      McCloskey, William B.; Wright, Glenn C.; Wright, Glenn; Kilby, Mike; Department of Plant Sciences; Yuma Mesa Agricultural Center (College of Agriculture, University of Arizona (Tucson, AZ), 1998-09)
      The effect of Roundup on lemon trees was evaluated by repeatedly spraying 0.5, 0.75, 1, 1.25, and 1.5 lb. a.i./acre on the bottom 20 to 24 inches of the tree canopies over a three year period. The Roundup applications caused significant leaf injury in the sprayed area of the canopies and there was also significant defoliation of branches at the higher Roundup rates in all three years of the study. In 1996, flower and fruitlet counts were not affected by the Roundup applications and the 1998 data were inconclusive. However, flower and fruitlet counts in 1997 in the sprayed zone of the canopy were significantly reduced by Roundup and the effect increased with increasing Roundup rate. The 1996 and 1997 yield data indicated that Roundup applied to the bottom 20 to 24 inches of the tree canopies did not significantly affect lemon yield. The preliminary data suggest that accidental drift or misapplication of Roundup on to lemon trees when spraying weeds on the orchard floor has no short-term effect on grove productivity.
    • Managing Vegetation on the Orchard Floor in Flood Irrigated Arizona Citrus Groves

      McCloskey, William B.; Wright, Glenn C.; Taylor, Kathryn C.; Wright, Glenn; Department of Plant Sciences; Yuma Mesa Agricultural Center (College of Agriculture, University of Arizona (Tucson, AZ), 1997-11)
      Several orchard floor management strategies were evaluated beginning in the fall of 1993 in experiments on the Yuma Mesa in a 'Limoneira 8A Lisbon' lemon grove and in a 'Valencia' orange grove at the University of Arizona Citrus Agricultural Center (CAC) in Waddell, Arizona. On the Yuma Mesa, disking provided satisfactory weed control except underneath the tree canopies where bermudagrass, purple nutsedge, and other weed species survived. Mowing the orchard floor suppressed broadleaf weed species allowing the spread of grasses, primarily bermudagrass. Pre-emergence (Solicam and Surffan) and post-emergence (Roundup and Torpedo) herbicides were used to control weeds in the clean culture treatment in Yuma. After three harvest seasons (1994-95 through 1996-97), the clean culture treatment resulted in greater yield than the other treatments. At the CAC, clean culture (in this location no pre -emergence herbicides were used,) mowed resident weeds, and Salina strawberry clover orchard floor management schemes were compared. Again the clean culture treatment yielded more than the mowed resident weeds. The yield of the strawberry clover treatment was somewhat less than the clean culture yield but not significantly less. The presence of cover crops or weeds on the orchard floor were found to have beneficial effects on soil nitrogen and soil organic matter content, but no effect on citrus leaf nutrient content. The decrease in yield in the mowed resident weed treatments compared to the clean culture treatment in both locations was attributed to competition for water.
    • Preliminary Results Regarding the Effects of Foliar Applied Roundup on Lemon Physiology and Yield

      McCloskey, William B.; Wright, Glenn C.; Wright, Glenn; Department of Plant Sciences; Yuma Mesa Agricultural Center (College of Agriculture, University of Arizona (Tucson, AZ), 1997-11)
      The effect of Roundup on lemon trees was evaluated by repeatedly spraying 0.5, 0.75, 1, 1.25, and 1.5 lb a.i/acre on the bottom 20 to 24 inches of the tree canopies. Leaf injury symptoms, flower and fruit counts, and yield data were collected The Roundup applications caused significant leaf injury in the sprayed area of the canopies and there was significant defoliation of branches at the higher Roundup rates. In 1996, flower and fruitier counts were not affected by the Roundup applications. However, flower and fruitier counts in 1997 in the sprayed zone of the canopy were significantly reduced by Roundup and the effect increased with increasing Roundup rate. The 1996 yield data indicated that the Roundup applications did not significantly affect lemon yield, however, the effect of Roundup on the 1997 flower and fruitier counts suggests that there may be a yield effect in 1997. The preliminary data suggest that accidental drift of Roundup on to lemon trees when spraying weeds on the orchard floor has no short-term effect on grove productivity but this conclusion must be substantiated by further data collection.